The present invention relates to devices for fastening railway rails and more particularly to improvements in these devices as concerns the electrical insulation of the rail and the ease with which the device is employed.
Among the systems for fastening railway rails to concrete sleepers or ties belonging to the "screwed" type of fasteners, that is to say fasteners clamped by bolts or coach-screws, the systems most often used with concrete sleepers employ a metal fastener having on one side a nose portion which bears on the flange of the rail and, on the opposite side, a loop portion or heel of cylindrical shape which bears in a cavity of complementary shape formed in the upper face of the sleeper. The insulation of the rail from the sleeper when required, in particular for signalling with the aid of the track circuit, is usually achieved by the interposition of the following elements:
An elastic and insulating sole or pad placed between the flange of the rail and the support face of the sleeper; PA1 A washer of insulating material comprising a spigot, this washer being placed between, on one hand, the metal fastener and, on the other, the bolt and nut assembly to avoid any contact between the fastener and the clamping means; PA1 A metal washer interposed between the nut and the insulating washer to ensure that the insulating washer, which is of a relatively fragile material, is not crushed or sheared under the effect of the very high pressure exerted by the nut; PA1 A pad or liner of insulating material interposed between the loop portion or heel of the fastener and the cavity of the sleeper. PA1 the loop portion has a generally cylindrical shape and has in section in a plane perpendicular to its axis, the shape of an arc of a circle which subtends an angle at the center exceeding 180.degree.; PA1 such arc of a circle has a radius slightly less than the radius of the adjacent cylindrical portion of the fastener; PA1 in the region of the loop portion, the insulating element has less thickness along two opposed lateral edges thereof; PA1 the spigot has at its free end at least one hooking means for hooking onto the fastener; PA1 the insulating element carries a metal plate which is held in position, for example by bosses which are in one piece with the remainder of the insulating element and engaged with the top of the plate.
The drawback of such a device resides above all in the multiplicity of the parts, the distribution and positioning of which require on the track laying site costly manpower and supervision and present a risk of bad workmanship and loss.
An effort has been made to overcome this drawback (French Pat. No. 1,282,099) by forming an assembly of the insulating washer and pad with the basic metal fastener by adhesion or by the use of vulcanized elastomers bonded to the steel of the fastener. But such a process is costly and requires much care to ensure a strong bonding which renders it unsuitable for mass-production on an industrial scale. The mere replacement of an insulating washer or pad is moreover impossible since it is necessary to replace a complete assembly of the fastening device and to return the metal fastener to the factory to provide it with a new insulating washer or pad.